1. Field of the Invention
The present invention relates to a semiconductor device.
2. Description of Related Art
A semiconductor device includes a semiconductor substrate, and a transistor formed on a principal surface of the semiconductor substrate. An element forming region and an element isolating region are provided on the principal surface. In the element forming region, an element such as a transistor or the like is provided. The element isolating region is provided for electrically separating the element forming region from other regions. The element isolating region is formed of an insulating material (for example, silicon oxide film or the like). The element forming region is surrounded by the element isolating region.
The element forming region includes a transistor forming region on which a transistor is provided. The transistor forming region includes a diffusion region (a source and drain region) and a channel forming region.
Generally, the element forming region and the element isolating region are formed of different materials. In this case, the channel forming region may be stressed by the element isolating region because of a difference in a rate of thermal expansion. The stress influences mobility of a carrier (an electron or hole) in the channel forming region.
As a related technique, a semiconductor integrated circuit is proposed in document 1 (Japanese patent publication JP-2007-311491A). This semiconductor integrated circuit has a CMOS circuit including a N-channel transistor and a P-channel transistor. In this semiconductor integrated circuit, one of the N-channel transistor and P-channel transistor has a gate-isolation structure, and the other has a shallow-trench-isolation structure. According to this semiconductor integrated circuit, one of the transistors is not stressed by STI, and the other is stressed by the STI to be changed in characteristics. Therefore, performance of the P-channel transistor and N-channel transistor can be efficiently improved.
The stress applied to the channel forming region by the element isolating region is depended on a distance between the channel forming region and the element isolating region. Accordingly, the mobility of carrier in the channel forming region is depended on the distance. As another related technique, in document 2 (Japanese patent publication JP-2007-27272), it is described that a drain current Idr is depended on a Gate-STI (X) that is a distance between a channel region and a STI region.